Components of electrical systems sometimes need to be interconnected using electrical connectors and/or switches to provide an overall, functioning system. These components may vary in size and complexity, depending on the type of system. For example, referring to FIG. 1, a system may include a backplane assembly comprising a backplane or motherboard 30 and a plurality of daughter boards 32 that may be interconnected using a connector 34, which may include an array of many individual pin connections for different traces etc., on the boards. For example, in telecommunications applications where the connector connects a daughter board to a backplane, each connector may include as many as 2000 pins or more. Alternatively, the system may include components that may be connected using a single-pin coaxial or other type of connector, and many variations in-between. Regardless of the type of electrical system, advances in technology have led electronic circuits and components to become increasingly smaller and more powerful. However, individual connectors are still, in general, relatively large compared to the sizes of circuit traces and components.
Referring to FIGS. 2a and 2b, there are illustrated perspective views of the backplane assembly of FIG. 1. FIG. 2a also illustrates an enlarged section of the male portion of connector 34, including a housing 36 and a plurality of pins 38 mounted within the housing 36. FIG. 2b illustrates an enlarged section of the female portion of connector 34 including a housing 40 that defines a plurality of openings 42 adapted to receive the pins 38 of the male portion of the connector. 34 including a housing 40 that defines a plurality of openings 42 adapted to receive the pins 38 of the male portion of the connector.
A portion of the connector 34 is shown in more detail in FIG. 3a. Each contact of the female portion of the connector includes a body portion 44 mounted within one of the openings (FIG. 2b, 42). A corresponding pin 38 of the male portion of the connector is adapted to mate with the body portion 44. Each pin 38 and body portion 44 includes a termination contact 48. As shown in FIG. 3b, the body portion 44 includes two cantilevered arms 46 adapted to provide an “interference fit” for the corresponding pin 38. In order to provide an acceptable electrical connection between the pin 38 and the body portion 44, the cantilevered arms 46 are constructed to provide a relatively high clamping force. Thus, a high normal force is required to mate the male portion of the connector with the female portion of the connector. This may be undesirable in many applications, as will be discussed in more detail below.
When the male portion of the conventional connector is engaged with the female portion, the pin 38 performs a “wiping” action as it slides between the cantilevered arms 46, requiring a high normal force to overcome the clamping force of the cantilevered arms and allow the pin 38 to be inserted into the body portion 44. There are three components of friction between the two sliding surfaces (the pin and the cantilevered arms) in contact, namely asperity interactions, adhesion and surface plowing. Surfaces, such as the pin 38 and cantilevered arms 46, that appear flat and smooth to the naked eye are actually uneven and rough under magnification. Asperity interactions result from interference between surface irregularities as the surfaces slide over each other. Asperity interactions are both a source of friction and a source of particle generation. Similarly, adhesion refers to local welding of microscopic contact points on the rough surfaces that results from high stress concentrations at these points. The breaking of these welds as the surfaces slide with respect to one another is a source of friction.
In addition, particles may become trapped between the contacting surfaces of the connector. For example, referring to FIG. 4a, there is illustrated an enlarged portion of the conventional connector of FIG. 3b, showing a particle 50 trapped between the pin 38 and cantilevered arm 46 of connector 34. The clamping force 52 exerted by the cantilevered arms must be sufficient to cause the particle to become partially embedded in one or both surfaces, as shown in FIG. 4b, such that electrical contact may still be obtained between the pin 38 and the cantilevered arm 46. If the clamping force 52 is insufficient, the particle 50 may prevent an electrical connection from being formed between the pin 38 and the cantilevered arm 46, which results in failure of the connector 34. However, the higher the clamping force 52, the higher must be the normal force required to insert the pin 38 into the body portion 44 of the female portion of the connector 34. When the pin slides with respect to the arms, the particle cuts a groove in the surface(s). This phenomenon is known as “surface plowing” and is a third component of friction.
Referring to FIG. 5, there is illustrated an enlarged portion of a contact point between the pin 38 and one of the cantilevered arms 46, with a particle 50 trapped between them. When the pin slides with respect to the cantilevered arm, as indicated by arrow 54, the particle 50 plows a groove 56 into the surface 58 of the cantilevered arm and/or the surface 60 of the pin. The groove 56 causes wear of the connector, and may be particularly undesirable in gold-plated connectors where, because gold is a relatively soft metal, the particle may plow through the gold-plating, exposing the underlying substrate of the connector. This accelerates wear of the connector because the exposed connector substrate, which may be, for example, copper, can easily oxidize. Oxidation can lead to more wear of the connector due to the presence of oxidized particles, which are very abrasive. In addition, oxidation leads to degradation in the electrical contact over time, even if the connector is not removed and re-inserted.
One conventional solution to the problem of particles being trapped between surfaces is to provide one of the surface with “particle traps.” Referring to FIGS. 6a–c, a first surface 62 moves with respect to a second surface 64 in a direction shown by arrow 66. When the surface 64 is not provided with particle traps, a process called agglomeration causes small particles 68 to combine as the surfaces move and form a large agglomerated particle 70, as illustrated in the sequence of FIGS. 6a–6c. This is undesirable, as a larger particle means that the clamping force required to break through the particle, or cause the particle to become embedded in one or both of the surfaces, so that an electrical connection can be established between surface 62 and surface 64 is very high. Therefore, the surface 64 may be provided with particle traps 72, as illustrated in FIGS. 6d–6g, which are small recesses in the surface as shown. When surface 62 moves over surface 64, the particle 68 is pushed into the particle trap 72, and is thus no longer available to cause plowing or to interfere with the electrical connection between surface 62 and surface 64. However, a disadvantage of these conventional particle traps is that it is significantly more difficult to machine surface 64 with traps than without, which adds to the cost of the connector. The particle traps also produce features that are prone to increased stress and fracture, and thus the connector is more likely to suffer a catastrophic failure than if there were no particle traps present.
An electrical switch is a basic element used for control of current in a circuit. An electrical switch (referred to hereafter as “switch”) is a device for making or breaking an electric circuit. Like electrical connectors, there are hundreds of different types of switches used in a variety of diverse applications. Precision snap acting switches, toggle switches and pushbutton switches are used in applications ranging from production machinery and submarines to medical instruments. Another type of switch, a rotary switch, is actuated by a rotational force applied to a shaft. An example of a rotary switch is an automotive directional indicator lever. Other types of switches, membrane, metal dome and conductive rubber switches, are commonly used in calculators, cell phones and computer keypads.
Despite the huge variation in switch technology, at a fundamental level the underlying physics and mechanics are similar. The contacts which make and break the circuit should have low resistance. This includes both the contact bulk resistance and the interfacial resistance between both contacts. Also, the contacts may have to open and close many times during its lifetime (over a million cycles is not uncommon) so contact friction and wear are important parameters. When a switch makes or breaks an electric circuit, an arc is produced at the contacts. The magnitude and duration of the arc is a function of many variables including AC or DC supply source, inductive or capacitive load, voltage and current magnitude, and rate at which the switch makes/breaks a circuit. If a large arc is produced, this can lead to contact damage.
The inventors have developed a novel conductive weave technology, which is also described in U.S. patent application Ser. No. 10/603,047, filed Jun. 24, 2003, U.S. patent application Ser. No. 10/375,481, filed Feb. 27, 2003, and U.S. patent application Ser. No. 10/273,241, filed Oct. 17, 2002, the entireties of which are herein incorporated by reference. The inventive conductive weave technology offers many advantages to switches, including lower contact resistance, lower friction, lower wear, and more redundant contact points, the combination of which results in smaller, more reliable, more rugged and longer lasting switches.